Manufacture of molybdenum-tungsten alloy



UNITED STATES PATENT OFFICE 1.

FREDERICK G. KEYES, OlF CAMBRIDGE, MASSACHUSETTS, ASSIGNOR TO COOPER HEWITT ELECTRIC COMPANY, A CORPORATION OF NEW JERSEY.

MANUFACTURE OF MOLYBDENUM-TUNGSTEN ALLOY.

110 Drawing. Original application filed October 16, 1915, Serial 110. 56,214. Divided and this applica- Specification of Letters Patent.

tion filed July 11, 1917. Serial No. 179,983.

To all whom it may concern:

Be it known that I, FREDERICK G. KEYES, a citizen of the United States, and resident of Cambridge, county of Middlesex, State of Massachusetts, have invented certain new and useful Improvements in the Manufacture of Molybdenum-Tungsten Alloy, of

making lamp filaments or resistance wire for electric'tube furnaces. For this purpose I have found that an alloy of pure tungsten with twenty per cent. of molybdenum, for example, is highly satisfactory. For other purposes and possibly also for the purpose of making a wire such as last described, other proportions of molybedenum and tungsten may be found usable. I may say that it appears to be only necessary that there should be enough of themolybdenum present, so that when the same is liquefied 'cles-at the beginning of the process.

by a heating process, there shall be enough liquid present to pull together the particles of powdered tungsten which, as will appear, are mixed with t e molybdenum oxid parti- The description herein will be concerned more particularly with the manufacture of .an

. alloy of eighty per cent. tungsten and twenty er cent. of molybdenum, although it is not intended to exclude other proportions of molybdenum in combination with tungsten, if manufactured in accordance with the process about to be described.

It is known that molybdenum has a melting point lying approximately 500 C. below the meltin point of tungsten. Now, when a bi-meta lic mixture of fine particles of molybdenum and tungsten is gradually heated by any suitable means, preferably by easing an electric current through it, the lbwer melting constituent will melt first, and if it'be present in suflicient quantity will, owing to its surface tension, tend to draw the mass of powdered material to-' gether into a coherent lngot. The followmg process 1s suited for producing conven- 1ently an alloy of molybdenum and tungsten. By taking quantities of chemically pure M00 and WO, and reducing the mixture to a metallic state, an alloy of the desired metallic Mo content will result. This content may be twenty per cent. molybdenum or any other percentage which is found preferable.

It is better to mix the oxids previously to reducing to the metallic state rather than to attempt to mix the metals after reduction, owlng to the fact that a much more uniform mechanlcal mixture can be produced in this way, on account of their being soft and capable of being reduced by means of a pestle or other grinding agent.

It will be understood that the oxids are first thoroughly ground and mixed. Thereafter they are reduced either by means of dry CO or dry H When reducing with H the reduction should be carried slowly to completlon at about 800 and finished at about 1000. Thec'oarseness of the mixture reduced by hydrogen depends on the speed of the gas stream. A very slow gas stream will require a longer time for the reduction and yield a coarser powder than a reduction carried out at the same temperature with a rapid stream of dry hydrogen. seem that the pressure of the water vapor which is not promptly carried oil, as it would be with a vigorous stream of hydrogen, causes a growth of small particles to larger particles by some alternate reduction and oxidation action.- For the purpose specially desired to be served by the present invention it is desirable to have fine and thoroughly reduced metal.

The metal, having been suitably reduced, is mixed with a little water and molded to a bar under pressure; During the drying It would.

of the molded bar the finer particlesundoubtedly oxidize superficially. -The dry bar is placed in a furnace maintained at about 1200 and through it a very slow stream ofdry hydrogen is caused to pass.

ficially oxidized particles. The bar roduced in the above manner when coole is further heated by the passage of the electric current until its temperature; has attained the melting point of molybdenum. At this temperature the molten molybdenum begins to alloy with the tungsten particles and, owing to the surface tension of the liquid molybdenum, the particles of tungsten are pulled together. In carrying out this process it is essential to maintain the bar at the proper temperature until contraction ceases.

The bar thus produced may be rolled into sheets at 800 to 900 (3. The material is quite soft while hot and may be drawn into wire by the ordinary drawlng process applied to most metals.

I prefer for many purposes, as has been stated, to make the proportions of molybdenum and tungsten respectively twenty per cent. and eighty per cent.

An alloy produced in the manner described and drawn into Wire is admirably suited to serve the purposes of a filament for electric lamps and of resistance for electric furnaces and like purposes.

This application is a division of my application Serial Number 56,214, filed October 16th, 1915.

I claim as my invention:

1. The step in the method of producing a bar of metallic alloy composed of molybdenum and tungsten which consists in subjecting a molded moistened bar of said metals to a drying process, applying to the dry bar a heat of about 1200 and passing through it a very slow stream of dry hydrogen.

2. The step in the method of producing 1200 and passing through it a very slow a stream of dry hydrogen for about an hour, and cooling the bar in H afterward further heating the bar .by passing an electric current therethrough until it has attained the melting point of molybdenum and maintaining the bar at approximately the temperature named until contraction ceases.

Signed at Cambridge in the county of Middlesex and .State of Massachusetts this 9th day of July A. D. 1917.

FREDERICK e. KEYES.

Witnesses WALTER HUMPHREYS, WILLIAM JACKSON. 

